Seven rarely-seen Dr Seuss stories from the 50s, which were tracked down by a Massachusetts dentist, will finally be published in book form this autumn.

Dr Seuss's art director Cathy Goldsmith was on eBay when she stumbled across a sale for tearsheets from 1950s magazines, purporting to be stories by the author, who was born Theodor Seuss Geisel in 1904. She bought the stories, and discovered that the seller, dentist Charles Cohen, was a huge collector of "Seussiana" and an avid Seuss scholar. She travelled to Springfield, Massachussetts, to meet him along with Random House vice-president and publisher Kate Klimo.

"His house was literally bursting at the seams with Seussiana: plush, toys, beer trays, puzzles, and a wide range of ephemera. Not only that, Dr Cohen was a fount of Seuss information, history, and theories about Ted's artistic process," said Klimo. "In short order, we had contracted Cohen to write what would become The Seuss, The Whole Seuss, and Nothing But the Seuss. Published in 2003, it was a nearly encyclopaedic look at Ted's career. But through it all, Charles always wanted to compile the stories he had found in various magazines."

Ten years later, The Bippolo Seed – described by the publisher as "the literary equivalent of buried treasure" – is lined up for publication in September. "These stories were published during what could arguably be called Dr Seuss's most fertile creative period, a time that would yield both Cat in the Hat and Grinch, a time when his theories about how to reach children through rhyme, rhythm, and a resonant combination of nonsense and sagacity, were coming into full bloom," said Klimo. "The stories are as good as anything in the already-published canon and readers of all ages are in for a treat."

The stories include The Strange Shirt Spot, the inspiration for the bathtub ring scene in The Cat in the Hat Comes Back ("'Have no fear of that ring,' / Laughed the Cat in the Hat. / 'Why, I can take cat rings / Off tubs. Just like that!' / Do you know how he did it? / WITH MOTHER'S WHITE DRESS! / Now the tub was all clean, / But her dress was a mess!") Gustav the Goldfish is an early, rhymed version of the Dr Seuss book A Fish Out of Water, about a fish that grows and grows, while The Bippolo Seed tells of a conniving feline (reminiscent of the Cat in the Hat, perhaps) who encourages an innocent duck to make a bad decision.

The book is completed with The Great Henry McBride, about a boy whose "far-flung career fantasies are only bested by those of the real Dr Seuss"; The Bear, the Rabbit, and the Zinniga-Zanniga, about a rabbit saved from a bear with a single eyelash; Steak for Supper, about fantastic creatures who follow a boy home for dinner; and Tadd and Todd, a story about twins.

Due out in late September from Random House in the US and HarperCollins in the UK, The Bippolo Seed and other lost stories will include an introduction from Cohen, explaining the significance of the stories in Dr Seuss's career. The author, who died in 1991 aged 87, won a Pulitzer for his contribution to American education. He wrote and illustrated 44 books, making his name in 1957 with The Cat in the Hat. Containing just 225 words, it was written following a challenge from his publisher: to write a fun story using the list of words first-grade schoolchildren needed to learn.